Red nitride phosphors

ABSTRACT

Provided according to embodiments of the invention are phosphor compositions that include Ca 1-x-y Sr x Eu y AlSiN 3 , wherein x is in a range of 0.50 to 0.99 and y is less than 0.013. Also provided according to embodiments of the invention are phosphor compositions that include Ca 1-x-y Sr x Eu y AlSiN 3 , wherein x is in a range of 0.70 to 0.99 and y is in a range of 0.001 and 0.025. Also provided are methods of making phosphors and light emitting devices that include a phosphor composition according to an embodiment of the invention.

FIELD OF THE INVENTION

The present invention relates phosphor compositions and to lightemitting devices that include phosphor compositions.

BACKGROUND

Light emitting diodes (“LEDs”) are well known solid state lightingdevices that are capable of generating light. LEDs generally include aplurality of semiconductor layers that may be epitaxially grown on asemiconductor or non-semiconductor substrate such as, for example,sapphire, silicon, silicon carbide, gallium nitride or gallium arsenidesubstrates. One or more semiconductor p-n junctions are formed in theseepitaxial layers. When a sufficient voltage is applied across the p-njunction, electrons in the n-type semiconductor layers and holes in thep-type semiconductor layers flow toward the p-n junction. As theelectrons and holes flow toward each other, some of the electrons will“collide” with a hole and recombine. Each time this occurs, a photon oflight is emitted, which is how LEDs generate light. The wavelengthdistribution of the light generated by an LED generally depends on thesemiconductor materials used and the structure of the thin epitaxiallayers that make up the “active region” of the device (i.e., the areawhere the electrons and holes recombine).

LEDs typically have a narrow wavelength distribution that is tightlycentered about a “peak” wavelength (i.e., the single wavelength wherethe radiometric emission spectrum of the LED reaches its maximum asdetected by a photo-detector). For example, the spectral powerdistributions of a typical LED may have a full width of, for example,about 10-30 nm, where the width is measured at half the maximumillumination (referred to as the full width half maximum or “FWHM”width). Accordingly, LEDs are often identified by their “peak”wavelength or, alternatively, by their “dominant” wavelength. Thedominant wavelength of an LED is the wavelength of monochromatic lightthat has the same apparent color as the light emitted by the LED asperceived by the human eye. Thus, the dominant wavelength differs fromthe peak wavelength in that the dominant wavelength takes into accountthe sensitivity of the human eye to different wavelengths of light.

As most LEDs are almost monochromatic light sources that appear to emitlight having a single color, LED lamps that include multiple LEDs thatemit light of different colors have been used in order to provide solidstate light emitting devices that generate white light. In thesedevices, the different colors of light emitted by the individual LEDchips combine to produce a desired intensity and/or color of whitelight. For example, by simultaneously energizing red, green and bluelight emitting LEDs, the resulting combined light may appear white, ornearly white, depending on the relative intensities of the source red,green and blue LEDs.

White light may also be produced by surrounding a single-color LED witha luminescent material that converts some of the light emitted by theLED to light of other colors. The combination of the light emitted bythe single-color LED that passes through the wavelength conversionmaterial along with the light of different colors that is emitted by thewavelength conversion material may produce a white or near-white light.For example, a single blue-emitting LED chip (e.g., made of indiumgallium nitride and/or gallium nitride) may be used in combination witha yellow phosphor, polymer or dye such as for example, cerium-dopedyttrium aluminum garnet (which has the chemical formulaY_(3-x)Ce_(x)Al₅O₁₂, and is commonly referred to as YAG:Ce), that“down-converts” the wavelength of some of the blue light emitted by theLED, changing its color to yellow. Blue LEDs made from indium galliumnitride exhibit high efficiency (e.g., external quantum efficiency ashigh as 60%). In a blue LED/yellow phosphor lamp, the blue LED chipproduces an emission with a dominant wavelength of about 450-465nanometers, and the phosphor produces yellow fluorescence with a peakwavelength of about 545-565 nanometers in response to the blue emission.Some of the blue light passes through the phosphor (and/or between thephosphor particles) without being down-converted, while a substantialportion of the light is absorbed by the phosphor, which becomes excitedand emits yellow light (i.e., the blue light is down-converted to yellowlight). The combination of blue light and yellow light may appear whiteto an observer. Such light is typically perceived as being cool white incolor. In another approach, light from a violet or ultraviolet emittingLED may be converted to white light by surrounding the LED withmulticolor phosphors or dyes. In either case, red-emitting phosphorparticles (e.g., (Ca_(1-x-y)Sr_(x)Eu_(y))AlSiN₃ based phosphor) may alsobe added to improve the color rendering properties of the light, i.e.,to make the light appear more “warm,” particularly when the single colorLED emits blue or ultraviolet light.

As noted above, phosphors are one known class of luminescent materials.A phosphor may refer to any material that absorbs light at onewavelength and re-emits light at a different wavelength in the visiblespectrum, regardless of the delay between absorption and re-emission andregardless of the wavelengths involved. Accordingly, the term “phosphor”may be used herein to refer to materials that are sometimes calledfluorescent and/or phosphorescent. In general, phosphors may absorblight having first wavelengths and re-emit light having secondwavelengths that are different from the first wavelengths. For example,“down-conversion” phosphors may absorb light having shorter wavelengthsand re-emit light having longer wavelengths.

LEDs are used in a host of applications including, for example,backlighting for liquid crystal displays, indicator lights, automotiveheadlights, flashlights, specialty lighting applications and even asreplacements for conventional incandescent and/or fluorescent lightingin general lighting and illumination applications. In many of theseapplications, it may be desirable to provide a lighting source thatgenerates light having specific properties.

SUMMARY

Provided according to some embodiments of the present invention arephosphor compositions that include Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃, whereinx is in a range of 0.50 to 0.99 and y is less than 0.013. Also providedaccording to embodiments of the invention are phosphor compositions thatinclude Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃, wherein x is in a range of 0.70 to0.99 and y is in a range of 0.001 and 0.025. In some embodiments of theinvention, the Sr to Eu ratio in the phosphor composition is in a rangeof 25 to 300. In some embodiments of the present invention, the phosphorcomposition is present in particulate form and at least 95% of theparticles are elongated. In some embodiments of the invention, thephosphor composition is present as particles having an average particlesize in a range of 4 μm to 20 μm.

In some embodiments of the present invention, the phosphor compositionincludes at least 1% by weight of a silicon aluminum oxynitride, such asSi₂Al₄O₄N₄. In some embodiments, the phosphor composition is present asa single crystal.

In some embodiments of the present invention, the phosphor compositionabsorbs light at a wavelength in a range of 350 and 530 nm and emitspeak frequencies at a wavelength in a range of 620 to 660 nm.

In some embodiments of the present invention, phosphor compositionsinclude Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ phosphor particles, wherein x<1 andy<1, and at least some of the Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ phosphorparticles are elongated. In some embodiments, x is in a range of 0.5 and0.99 and y is in a range of 0.001 and 0.025. In some embodiments, 50% ormore of the Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ phosphor particles areelongated, in some embodiments, 75% or more of theCa_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ phosphor particles are elongated, and insome embodiments, 95% or more of the Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃phosphor particles are elongated.

Also provided according to embodiments of the present invention arelight emitting devices that include a solid state lighting source; and aphosphor composition according to an embodiment of the invention. Insome embodiments of the invention, the LED emits a warm white lighthaving a correlated color temperature between about 2700K and 5400K. Insome embodiments, the light emitting device has a CRI value of greaterthan 90. In some embodiments, the light emitting device also includes agreen and/or yellow phosphor.

Also provided according to embodiments of the invention are methods offorming a phosphor composition. In some embodiments, the methods includemixing nitrides of calcium, strontium, aluminum and silicon with aeuropium source composition to form a precursor mixture, heating theprecursor mixture to a temperature in a range of 1500 and 1800° C. inthe presence of forming gas, in a refractory crucible, to produce aphosphor composition according to an embodiment of the invention.

In some embodiments of the invention, the precursor mixture is heated ina substantial absence of water and oxygen. In some embodiments of theinvention, the refractory crucible is substantially inert in thepresence of the forming gas mixture. In some embodiments, the forminggas dynamically flows around the refractory crucible. In someembodiments, the precursor mixture is heated at a first temperature forat least 0.5 hours, heated to a second temperature for at least 0.5hours, and then heated to a third temperature for at least 0.5 hours. Inparticular embodiments, the first temperature is 800° C., the secondtemperature is 1200° C. and the third temperature is 1800° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top perspective of an apparatus that may be used to form aphosphor composition according to an embodiment of the invention.

FIG. 2 shows an apparatus that may be used to form a phosphorcomposition according to an embodiment of the invention.

FIG. 3 shows the forming gas flow in an apparatus that may be used toform a phosphor composition according to an embodiment of the invention.

FIG. 4 illustrates the variation in relative brightness for phosphorcompositions according to some embodiments of the present invention.

FIG. 5 illustrates the variation in relative color shift for phosphorcompositions according to some embodiments of the present invention.

FIG. 6 provides a three dimensional graph showing the variation inrelative color and relative brightness as a function of the Sr to Euratio for phosphor compositions according to some embodiments of thepresent invention. The arrow within the shaded region is provided toguide the eye in the third dimension.

FIG. 7A provides a three dimensional graph showing the variation inrelative color and relative brightness as a function of the Srconcentration for phosphor compositions according to some embodiments ofthe present invention. The arrow within the shaded region is provided toguide the eye in the third dimension.

FIG. 7B provides a three dimensional graph showing the variation inrelative color and relative brightness as a function of the Euconcentration for phosphor compositions according to some embodiments ofthe present invention. The arrow within the shaded region is provided toguide the eye in the third dimension.

FIGS. 8A-8D are various views of a solid state light emitting deviceaccording to embodiments of the present invention.

FIGS. 9A-9E are sectional views illustrating fabrication steps that maybe used to apply a phosphor composition to an LED chip wafer accordingto embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. However, this invention should not be construed aslimited to the embodiments set forth herein. Rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the invention to those skilled in theart. In the drawings, the thickness of layers and regions areexaggerated for clarity. Like numbers refer to like elements throughout.As used herein the term “and/or” includes any and all combinations ofone or more of the associated listed items.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that, when used in thisspecification, the terms “comprises” and/or “including” and derivativesthereof, specify the presence of stated features, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, operations, elements, components, and/or groupsthereof.

It will be understood that when an element such as a layer, region orsubstrate is referred to as being “on” or extending “onto” anotherelement, it can be directly on or extend directly onto the other elementor intervening elements may also be present. In contrast, when anelement is referred to as being “directly on” or extending “directlyonto” another element, there are no intervening elements present. Itwill also be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions and/orlayers, these elements, components, regions and/or layers should not belimited by these terms. These terms are only used to distinguish oneelement, component, region or layer from another element, component,region or layer. Thus, a first element, component, region or layerdiscussed below could be termed a second element, component, region orlayer without departing from the teachings of the present invention.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother element as illustrated in the figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the figures. Forexample, if the device in the figures is turned over, elements describedas being on the “lower” side of other elements would then be oriented on“upper” sides of the other elements. The exemplary term “lower”, cantherefore, encompasses both an orientation of “lower” and “upper,”depending on the particular orientation of the figure.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of this specification andthe relevant art and will not be interpreted in an idealized or overlyformal sense unless expressly so defined herein.

All patents and patent applications referred to herein are incorporatedby reference herein in their entirety. In case of conflictingterminology or scope, the present application is controlling.

As used herein, the term “solid state light emitting device” may includea light emitting diode, laser diode and/or other semiconductor devicewhich includes one or more semiconductor layers, which may includesilicon, silicon carbide, gallium nitride and/or other semiconductormaterials, an optional substrate which may include sapphire, silicon,silicon carbide and/or other microelectronic substrates, and one or morecontact layers which may include metal and/or other conductivematerials. The design and fabrication of solid state light emittingdevices are well known to those skilled in the art. The expression“light emitting device,” as used herein, is not limited, except that itbe a device that is capable of emitting light.

Solid state light emitting devices according to embodiments of theinvention may include III-V nitride (e.g., gallium nitride) based LEDsor lasers fabricated on a silicon carbide or gallium nitride substratessuch as those devices manufactured and sold by Cree, Inc. of Durham,N.C. Such LEDs and/or lasers may (or may not) be configured to operatesuch that light emission occurs through the substrate in a so-called“flip chip” orientation. Solid state light emitting devices according toembodiments of the present invention include both vertical devices witha cathode contact on one side of the chip, and an anode contact on anopposite side of the chip and devices in which both contacts are on thesame side of the device. Some embodiments of the present invention mayuse solid state light emitting devices, device packages, fixtures,luminescent materials/elements, power supplies, control elements, and/ormethods such as described in U.S. Patent Nos. 7,564,180; 7,456,499;7,213,940; 7,095,056; 6,958,497; 6,853,010; 6,791,119; 6,600,175,6,201,262; 6,187,606; 6,120,600; 5,912,477; 5,739,554; 5,631,190;5,604,135; 5,523,589; 5,416,342; 5,393,993; 5,359,345; 5,338,944;5,210,051; 5,027,168; 5,027,168; 4,966,862, and/or 4,918,497, and U.S.Patent Application Publication Nos. 2009/0184616; 2009/0080185;2009/0050908; 2009/0050907; 2008/0308825; 2008/0198112; 2008/0179611,2008/0173884, 2008/0121921; 2008/0012036; 2007/0253209; 2007/0223219;2007/0170447; 2007/0158668; 2007/0139923, and/or 2006/0221272.

Provided according to embodiments of the invention are phosphorcompositions that include Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃, wherein x is ina range of 0.50 to 0.99 and y is less than 0.013. In particularembodiments of the invention, y is in a range of 0.001 to 0.013, and inparticular embodiments, in a range of 0.001 to 0.012. Provided accordingto embodiments of the invention are phosphor compositions that includeCa_(1-x-y)Sr_(x)Eu_(y)AlSiN₃, wherein x is in a range of 0.70 to 0.99and y is in a range of 0.001 and 0.025. Furthermore, in someembodiments, x in a range of 0.71 to 0.99, and in particularembodiments, in a range of 0.70 to 0.90. In some embodiments of theinvention, the Sr to Eu ratio in the phosphor composition is in a rangeof 25 to 300.

Although the Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ may include a minimal amountof oxygen, there is not enough oxygen present in the composition toaffect the crystal structure from that formed by the nitride. Thus, theCa_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ is not an oxynitride phosphor. Personsskilled in this art recognize that there is no bright line or exactboundary that defines the amount of oxygen present that causes thecomposition to be categorized as an oxynitride rather than a nitride,but generally speaking in a nitride phosphor, only very small amounts ofoxygen are present; e.g., less than five percent (5%) as compared to theamount of nitrogen present. The phosphor composition may include morethan one type of phosphor having the formula ofCa_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ and/or may include other phosphors or otherluminophoric compositions in combination (both within the same phosphorcomposition or in another composition in a device described herein) withthe Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃.

Although the Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ is not an oxynitride phosphor,in some embodiments of the invention, the Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃phosphor composition includes at least 1% by weight of a separatesilicon aluminum oxynitride phase. In some embodiments, the siliconaluminum oxynitride phase includes Si₂Al₄O₄N₄.

The phosphor may be present in any suitable form, including but notlimited to particles, blocks, or other known phosphor structures. Insome embodiments, the phosphor composition is present as particleshaving an average particle size in a range of about 2.0 μm and 25 μm.The mixture may be pulverized in conventional fashion for use as may bedesired or necessary. The size of the pulverized particles depends onthe end application and in most circumstances can be chosen by the enduser. The particles may also be obtained in any suitable shape,including elongated, spherical and/or semi-spherical. In someembodiments, 50, 75 or 95% or more of the particles in the phosphorcomposition are elongated. In some embodiments, 50, 75 or 95% or more ofthe particles in the phosphor composition are spherical or substantiallyspherical. It has been discovered that in some embodiments, as thecalcium concentration decreases, the particles may become moreelongated.

In some embodiments of the present invention, phosphor compositionsinclude Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ phosphor particles, wherein x<1 andy<1, and at least some of the Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ phosphorparticles are elongated. In some embodiments, x is in a range of 0.5 and0.99 and y is in a range of 0.001 and 0.025. In some embodiments, 50% ormore of the Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ phosphor particles areelongated, in some embodiments, 75% or more of theCa_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ phosphor particles are elongated, and insome embodiments, 95% or more of the Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃phosphor particles are elongated. Post-processing of the phosphor mayalso be performed, such as, for example, those methods described in U.S.Patent Application No. 12/466,782, filed May 15, 2009 and U.S. patentapplication Ser. No. ______, filed Jun. 3, 2011, entitled Red NitridePhosphors, the contents of which are incorporated herein by reference intheir entirety.

Also provided according to embodiments of the invention are methods offorming phosphor compositions. In some embodiments, such methods includemixing nitrides of calcium, strontium, aluminum and silicon with aeuropium source composition to form a precursor mixture, and thenheating the precursor mixture in the presence of forming gas to atemperature that is sufficient to produce the phosphor but less than atemperature at which the precursor compositions or the phosphor woulddecompose or react with the crucible. The reaction is carried out for atime sufficient to produce a phosphor composition that will down convertphotons in the blue and ultraviolet regions of the spectrum (i.e.,between about 430 and 480 nm) into photons in the longer-wavelengthregions of the visible spectrum (i.e., between about 530 and 750 nm).Persons skilled in this art will recognize that the boundaries forcolors in the visible spectrum are used descriptively rather than in alimiting sense.

In some embodiments, this heating of the precursor mixture is performedin the substantial absence of water and oxygen. In some embodiments, theprecursor mixture is heated to a temperature in a range of 1500° C. and1800° C.

As used herein, the phrase “europium source composition” refers to acomposition that will produce europium as the activator cation in thecrystal lattice of the phosphor under the reaction conditions set forthherein. For example, in some embodiments, europium fluoride is theeuropium source composition.

As used herein, the term “forming gas” refers to a mixture of nitrogenand hydrogen gas. In some embodiments, forming gas has a relatively highnitrogen content. For example, in some cases, forming gas includesnitrogen at a concentration in a range of 90% to 95% by volume, and thehydrogen is present at a concentration in a range of 5% to 10%.

In some embodiments of the invention, the mixture is heated at or nearatmospheric pressure.” As used herein, the term “at or near atmosphericpressure” refers to a pressure that does not require high pressureequipment.

In some embodiments, the precursor mixture is heated in a refractorycrucible. In some embodiments, the refractory crucible is substantiallyinert in the presence of the farming gas mixture. For example, in someembodiments, the refractory crucible includes molybdenum. Synthesis of aphosphor in an inappropriate crucible material can reduce the opticalperformance of a phosphor. Such degradation usual results from somereaction between the crucible material and the reactants. For example,when aluminum oxide crucibles were used in reactions similar to thosedescribed herein, the oxygen from the crucible tended to be incorporatedinto the resulting phosphor powder which in turn demonstrated poorluminescent qualities. As examples, crucibles of tungsten (W) andmolybdenum (Mo) have been determined to be advantageous in someembodiments. Tungsten and molybdenum are refractory metals; they canwithstand high temperatures and are inert under the correct atmospheres.

In some embodiments of the invention, the heating steps (firing) iscarried out in several steps at different temperatures with appropriateramping in between temperatures. In some embodiments of the invention,the precursor mixture is heated at a first temperature for at least 0.5hours, heated to a second temperature for at least 0.5 hours, and thenheated to a third temperature for at least 0.5 hours. In someembodiments, the temperature is ramped at 350° C. per hour betweenheating steps. In some embodiments, the first temperature is 800° C.,the second temperature is 1200° C. and the third temperature is 1800° C.

Any suitable method of forming the phosphor compositions may be used.However, some methods that may be useful are found in U.S. patentapplication Ser. No. 12/271,945, filed Nov. 17, 2008, the contents ofwhich are hereby incorporated by reference herein in their entirety. Insome embodiments, the phosphor composition is formed by the followingmethod. FIG. 1 is a top perspective view of a relatively large aluminacrucible broadly designated at 10. In some embodiments of the invention,nitrides of calcium (Ca₃N₂), nitrides of strontium (Sr₂N), nitrides ofaluminum (AlN), and nitrides of silicon (Si₃N₄) and europium fluorideare mixed according to the target stoichiometry in a glove box (notshown) which is essentially free of water and oxygen. The powders arethen loaded into the tungsten or molybdenum crucible shown as thecircular crucible 11 resting on the floor 12 of the large aluminacrucible 10. A gas flow tube 13 projects into the interior of thecrucible 10 through the cylindrical wall 14.

FIG. 2 shows the crucible 10 and a lid 15 and the external portion ofthe gas tube 16. The alumina crucible 10 is placed in a box furnacebroadly designated at 17. The alumina crucible 10 is not alwaysnecessary. If the furnace itself is fitted to contain the forming gasatmosphere, the alumina crucible 10 illustrated in the drawings can beoptional. The tube 16 is typically formed of a ceramic material, whichis likewise selected to be unaffected by the forming gas or by any ofthe compositions used to form the phosphor or by the phosphor itself.The box furnace 17 is then used to heat the materials using the thermalcycle described earlier. FIG. 3 is a cross-sectional view of the aluminacrucible 10 illustrating the cylindrical wall 14 and the lid 15. Theceramic tube 16, 13 extends through the wall 14 to the interior of thealumina crucible 10 and the arrows schematically illustrate the forminggas flowing over the tungsten or molybdenum crucible 11. Otherconfigurations may be used, including whereby alumina crucible is moreclosely fitted around the tungsten or molybdenum crucible 11.

As shown in FIG. 3, the crucible is surrounded by a dynamic flow offorming gas (e.g., 95% N₂/5% H₂) through the use of a ceramic tubinserted into the larger alumina crucible. The box furnace is heated to800° C. for 1 hour, then heated to 1200° C. for one hour, and thenheated to 1800° C. for 2 hours. The temperature ramping rate is 350° C.per hour. This process may produce a Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃phosphor composition according to an embodiment of the invention thatalso includes a separate phase that includes at least 1% of siliconaluminum oxynitride.

Under these conditions, the phosphor can be synthesized at or nearambient (i.e., atmospheric) pressures, thus offering significant processadvantages by avoiding the need for high pressure techniques andequipment. It is believed that the substantial absence of oxygen andwater, but not the complete absence, allows of the silicon aluminumoxynitride phase to form. It has been surprisingly discovered thatphosphors that include this phase may have desirable optical properties.

Also provided according to embodiments of the invention are lightemitting devices that include a phosphor composition described herein.As such, in some embodiments, light emitting devices include a solidstate lighting source and a phosphor composition according to anembodiment of the invention.

FIGS. 4 and 5 provide graphs of relative brightness and relative coloras a function of the europium and strontium concentration for phosphorsaccording to embodiments of the present invention. It has surprisinglybeen discovered that for a given Sr concentration, as the europiumconcentration decreases, the brightness and color shift increases.Additionally, for a given Eu concentration, as the Sr concentrationincreases, the brightness and color shift increase. FIG. 6 shows thevariation in relative brightness and relative color as a function of theSr to Eu ratio. As the Sr to Eu ratio is increased, the relativebrightness also increases. FIG. 7A shows the variation in relativebrightness and relative color as a function of the Sr concentration.FIG. 7B shows the variation in relative brightness and relative color asa function of the Eu concentration. This is discussed further in U.S.application Ser. No. ______, filed Jun. 3, 2011 entitled Methods ofDetermining and Making Red Nitride Phosphor Compositions, the contentsof which are incorporated herein by reference in their entirety.

A solid state light emitting device 30 will now be described thatincludes a phosphor composition according to embodiments of the presentinvention with reference to FIGS. 8A-8D. The solid state light emittingdevice 30 comprises a packaged LED. In particular, FIG. 8A is aperspective view of the solid state light emitting device 30 without alens thereof. FIG. 8B is a perspective view of the device 30 viewed fromthe opposite side. FIG. 8C is a side view of the device 30 with a lenscovering the LED chip. FIG. 8D is a bottom perspective view of thedevice 30.

As shown in FIG. 8A, the solid state light emitting device 30 includes asubstrate/submount (“submount”) 32 on which a single LED chip or “die”34 is mounted. The submount 32 can be formed of many different materialssuch as, for example, aluminum oxide, aluminum nitride, organicinsulators, a printed circuit board (PCB), sapphire or silicon. The LED34 can have many different semiconductor layers arranged in differentways. LED structures and their fabrication and operation are generallyknown in the art and hence are only briefly discussed herein. The layersof the LED 34 can be fabricated using known processes such as, forexample, metal organic chemical vapor deposition (MOCVD). The layers ofthe LED 34 may include at least one active layer/region sandwichedbetween first and second oppositely doped epitaxial layers all of whichare formed successively on a growth substrate. Typically, many LEDs aregrown on a growth substrate such as, for example, a sapphire, siliconcarbide, aluminum nitride (AlN), or gallium nitride (GaN) substrate toprovide a grown semiconductor wafer, and this wafer may then besingulated into individual LED dies, which are mounted in a package toprovide individual packaged LEDs. The growth substrate can remain aspart of the final singulated LED or, alternatively, the growth substratecan be fully or partially removed. In embodiments where the growthsubstrate remains, it can be shaped and/or textured to enhance lightextraction.

It is also understood that additional layers and elements can also beincluded in the LED 34, including but not limited to buffer, nucleation,contact and current spreading layers as well as light extraction layersand elements. It is also understood that the oppositely doped layers cancomprise multiple layers and sub-layers, as well as super latticestructures and interlayers. The active region can comprise, for example,a single quantum well (SQW), multiple quantum well (MQW), doubleheterostructure or super lattice structure. The active region and dopedlayers may be fabricated from different material systems, including, forexample, Group-III nitride based material systems such as GaN, aluminumgallium nitride (AlGaN), indium gallium nitride (InGaN) and/or aluminumindium gallium nitride (AlInGaN). In some embodiments, the doped layersare GaN and/or AlGaN layers, and the active region is an InGaN layer.

The LED 34 may be an ultraviolet, violet or blue LED that emitsradiation with a dominant wavelength in a range of about 380 to about475 nm.

The LED 34 may include a conductive current spreading structure 36 onits top surface, as well as one or more contacts 38 that are accessibleat its top surface for wire bonding. The spreading structure 36 andcontacts 38 can both be made of a conductive material such as Au, Cu,Ni, In, Al, Ag or combinations thereof, conducting oxides andtransparent conducting oxides. The current spreading structure 36 maycomprise conductive fingers 37 that are arranged in a pattern on the LED34 with the fingers spaced to enhance current spreading from thecontacts 38 into the top surface of the LED 34. In operation, anelectrical signal is applied to the contacts 38 through a wire bond asdescribed below, and the electrical signal spreads through the fingers37 of the current spreading structure 36 into the LED 34. Currentspreading structures are often used in LEDs where the top surface isp-type, but can also be used for n-type materials.

The LED 34 may be coated with a phosphor composition 39 according toembodiments of the present invention. It will be understood that thephosphor composition 39 may comprise any of the phosphor compositionsdiscussed in the present disclosure.

The phosphor composition 39 may be coated on the LED 34 using manydifferent methods, with suitable methods being described in U.S. patentapplications Ser. Nos. 11/656,759 and 11/899,790, both entitled WaferLevel Phosphor Coating Method and Devices Fabricated Utilizing Method.Alternatively the phosphor composition 39 may be coated on the LED 34using other methods such an electrophoretic deposition (EPD), with asuitable EPD method described in U.S. patent application Ser. No.11/473,089 entitled Close Loop Electrophoretic Deposition ofSemiconductor Devices. One exemplary method of coating the phosphorcomposition 39 onto the LED 34 is described herein with reference toFIGS. 9A-9E.

An optical element or lens 70 (see FIGS. 8C-8D) is formed on the topsurface 40 of the submount 32, over the LED 34, to provide bothenvironmental and/or mechanical protection. The lens 70 can be moldedusing different molding techniques such as those described in U.S.patent applications Ser. No. 11/982,275 entitled Light Emitting DiodePackage and Method for Fabricating Same. The lens 70 can be manydifferent shapes such as, for example, hemispheric. Many differentmaterials can be used for the lens 70 such as silicones, plastics,epoxies or glass. The lens 70 can also be textured to improve lightextraction and/or scattering particles. In some embodiments, the lens 70may comprise the phosphor composition 39 and/or may be used to hold aphosphor composition 39 in place over the LED 34 instead of and/or inaddition to coating a phosphor composition 39 directly onto the LED chip34.

The solid state light emitting device 30 may comprise an LED packagehaving different sizes or footprints. In some embodiments, the surfacearea of the LED chip 34 may cover more than 10% or even 15% of thesurface area of the submount 32. In some embodiments, the ratio of thewidth W of the LED chip 34 to the diameter D (or width D, for squarelens) of the lens 70 may be greater than 0.5. For example, in someembodiments, the solid state light emitting device 30 may comprise anLED package having a submount 32 that is approximately 3.45 mm squareand a hemispherical lens having a maximum diameter of approximately 2.55mm The LED package may be arranged to hold an LED chip that isapproximately 1.4 mm square. In this embodiment, the surface area of theLED chip 34 covers more than 16% of the surface area of the submount 32.

The top surface 40 of the submount 32 may have patterned conductivefeatures that can include a die attach pad 42 with an integral firstcontact pad 44. A second contact pad 46 is also included on the topsurface 40 of the submount 32 with the LED 34 mounted approximately atthe center of the attach pad 42. The attach pad 42 and first and secondcontact pads 44, 46 may comprise metals or other conductive materialssuch as, for example, copper. The copper pads 42, 44, 46 may be platedonto a copper seed layer that is, in turn, formed on a titanium adhesionlayer. The pads 42, 44, 46 may be patterned using standard lithographicprocesses. These patterned conductive features provide conductive pathsfor electrical connection to the LED 34 using known contacting methods.The LED 34 can be mounted to the attach pad 42 using known methods andmaterials.

A gap 48 (see FIG. 8A) is included between the second contact pad 46 andthe attach pad 42 down to the surface of the submount 32. An electricalsignal is applied to the LED 34 through the second pad 46 and the firstpad 44, with the electrical signal on the first pad 44 passing directlyto the LED 34 through the attach pad 42 and the signal from the secondpad 46 passing into the LED 34 through wire bonds. The gap 48 provideselectrical isolation between the second pad 46 and attach pad 42 toprevent shorting of the signal applied to the LED 34.

Referring to FIGS. 8C and 8D, an electrical signal can be applied to thepackage 30 by providing external electrical contact to the first andsecond contact pads 44, 46 via first and second surface mount pads 50,52 that are formed on the back surface 54 of the submount 32 to be atleast partially in alignment with the first and second contact pads 44,46, respectfully. Electrically conductive vias 56 are formed through thesubmount 32 between the first mounting pad 50 and the first contact pad44, such that a signal that is applied to the first mounting pad 50 isconducted to first contact pad 44. Similarly, conductive vias 56 areformed between the second mounting pad 52 and second contact pad 46 toconduct an electrical signal between the two. The first and secondmounting pads 50, 52 allow for surface mounting of the LED package 30with the electrical signal to be applied to the LED 34 applied acrossthe first and second mounting pads 50, 52.

The pads 42, 44, 46 provide extending thermally conductive paths toconduct heat away from the LED 34. The attach pad 42 covers more of thesurface of the submount 32 than the LED 34, with the attach padextending from the edges of the LED 34 toward the edges of the submount32. The contact pads 44, 46 also cover the surface of the submount 32between the vias 56 and the edges of the submount 32. By extending thepads 42, 44, 46, the heat spreading from the LED 34 may be improved,which may improve the operating life of the LED and/or allow for higheroperating power.

The LED package 30 further comprises a metalized area 66 on the backsurface 54 of the submount 32, between the first and second mountingpads 50, 52. The metalized area 66 may be made of a heat conductivematerial and may be in at least partial vertical alignment with the LED34. In some embodiments, the metalized area 66 is not in electricalcontact with the elements on top surface of the submount 32 or the firstand second mounting pads 50, 52 on the back surface of the submount 32.Although heat from the LED is spread over the top surface 40 of thesubmount 32 by the attach pad 42 and the pads 44, 46, more heat willpass into the submount 32 directly below and around the LED 34. Themetalized area 66 can assist with this dissipation by allowing this heatto spread into the metalized area 66 where it can dissipate morereadily. The heat can also conduct from the top surface 40 of thesubmount 32, through the vias 56, where the heat can spread into thefirst and second mounting pads 50, 52 where it can also dissipate.

It will be appreciated that FIGS. 8A-8D illustrate one exemplarypackaged LED that may include phosphor compositions according toembodiments of the present invention. Additional exemplary packaged LEDsare disclosed in, for example, U.S. Provisional Patent Application No.61/173,550, filed Apr. 28, 2009, the entire contents of which areincorporated by reference herein as if set forth in its entirety. Itwill likewise be appreciated that the phosphor compositions according toembodiments of the present invention may be used with any other packagedLED structures.

As noted above, in some embodiments, the phosphor compositions accordingto embodiments of the present invention may be directly coated onto asurface of a semiconductor wafer before the wafer is singulated intoindividual LED chips. One such process for applying the phosphorcomposition will now be discussed with respect to FIGS. 9A-9E. In theexample of FIGS. 9A-9E, the phosphor composition is coated onto aplurality of LED chips 110. In this embodiment, each LED chip 110 is avertically-structured device that has a top contact 124 and a bottomcontact 122.

Referring to FIG. 9A, a plurality of LED chips 110 (only two are shown)are shown at a wafer level of their fabrication process (i.e., beforethe wafer has been separated/singulated into individual LED chips). Eachof the LED chips 110 comprises a semiconductor LED that is formed on asubstrate 120. Each of the LED chips 110 has first and second contacts122, 124. The first contact 122 is on the bottom of the substrate 120and the second contact 124 is on the top of the LED chip 110. In thisparticular embodiment, the top contact 124 is a p-type contact and thecontact 122 on the bottom of the substrate 120 is an n-type contact.However, it will be appreciated that in other embodiments, the contacts122, 124 may be arranged differently. For example, in some embodiments,both the contact 122 and the contact 124 may be formed on an uppersurface of the LED chip 110.

As shown in FIG. 9B, a conductive contact pedestal 128 is formed on thetop contact 124 that is utilized to make electrical contact to thep-type contact 124 after the LED chips 110 are coated with a phosphorcomposition. The pedestal 128 can be formed of many differentelectrically conductive materials and can be formed using many differentknown physical or chemical deposition processes such as electroplating,mask deposition (e-beam, sputtering), electroless plating, or studbumping. The height of the pedestal 128 can vary depending on thedesired thickness of the phosphor composition and should be high enoughto match or extend above the top surface of the phosphor compositioncoating from the LED.

As shown in FIG. 9C, the wafer is blanketed by a phosphor compositioncoating 132 that covers each of the LED chips 110, the contacts 122, andthe pedestal 128. The phosphor composition coating 132 may comprise abinder and a phosphor composition according to an embodiment of theinvention. The material used for the binder may be a material that isrobust after curing and substantially transparent in the visiblewavelength spectrum such as, for example, a silicone, epoxy, glass,inorganic glass, spin-on glass, dielectrics, BCB, polymides, polymersand the like. The phosphor composition coating 132 can be applied usingdifferent processes such as spin coating, dispensing, electrophoreticdeposition, electrostatic deposition, printing, jet printing or screenprinting. Yet another suitable coating technique is disclosed in U.S.patent application Ser. No. 12/717,048, filed Mar. 3, 2010, the contentsof which are incorporated herein by reference. The phosphor compositioncoating 132 can then be cured using an appropriate curing method (e.g.,heat, ultraviolet (UV), infrared (IR) or air curing).

Different factors determine the amount of LED light that will beabsorbed by the phosphor composition coating 132 in the final LED chips110, including but not limited to the size of the phosphor particles,the percentage of phosphor loading, the type of binder material, theefficiency of the match between the type of phosphor and wavelength ofemitted light, and the thickness of the phosphor composition coating132. It will be understood that many other phosphors can used alone orin combination to achieve the desired combined spectral output.

Different sized phosphor particles can be used including, but notlimited to, 10-100 nanometer (nm)-sized particles to 20-30 μm sizedparticles, or larger. Smaller particle sizes typically scatter and mixcolors better than larger sized particles to provide a more uniformlight. Larger particles are typically more efficient at converting lightcompared to smaller particles, but emit a less uniform light. In someembodiments, the phosphor particles may range in size from about 1micron to about 30 microns, with about half of the particles being frombetween about 4 microns to about 20 microns. In some embodiments, atleast half of the particles of the phosphors may have a size (diameter)in the range between 2 microns and 20 microns. Different sized phosphorscan be included in the phosphor composition coating 132 as desiredbefore it is applied such that the end coating 132 can have the desiredcombination of smaller sizes to effectively scatter and mix the light,and larger sizes to efficiently convert the light.

The coating 132 can also have different concentrations or loading ofphosphor materials in the binder, with a typical concentration being inrange of 30-70% by weight. In one embodiment, the phosphor concentrationis approximately 65% by weight, and is may be generally uniformlydispersed throughout the binder. In other embodiments the coating 132can comprise multiple layers of different concentrations or types ofphosphors, and the multiple layers can comprise different bindermaterials. One or more of the layers can be provided without phosphors.For example, a first coat of clear silicone can be deposited followed byphosphor loaded layers. As another example, the coating may comprise,for example, a two layer coating that includes a first layer having onetype of phosphor on the LED chips 110, and a second layer directly onthe first layer that includes a second type of phosphor. Numerous otherlayer structures are possible, including multi-layers that includemultiple phosphors in the same layer, and intervening layers or elementscould also be provided between layers and/or between the coating and theunderlying LED chips 110.

After the initial coating of the LED chips 110 with the phosphorcomposition coating 132, further processing is needed to expose thepedestal 128. Referring now the FIG. 9D, the coating 132 is thinned orplanarized to expose the pedestals 128 through the top surface of thecoating 132. The thinning process exposes the pedestals 128, planarizesthe coating 132 and allows for control of the final thickness of thecoating 132. Based on the operating characteristics of the LEDs 110across the wafer and the properties of the phosphor (or fluorescent)material selected, the end thickness of the coating 132 can becalculated to reach a desired color point/range and still expose thepedestals 128. The thickness of the coating 132 can be uniform ornon-uniform across the wafer. Any suitable coating thickness may beused. However, in some embodiments, the coating is less than 1 μm, insome embodiments, less than 500 μm, in some embodiments, less than 100μm, in some embodiments, less than 10 μm.

As shown in FIG. 9E, after the coating 132 is applied, the individualLED chips 110 can be singulated from the wafer using known methods suchas dicing, scribe and breaking, or etching. The singulating processseparates each of the LED chips 110 with each having substantially thesame thickness of coating 132, and as a result, substantially the sameamount of phosphor and thus substantially the same emissioncharacteristics. Following singulation of the LED chips 110, a layer ofcoating 132 remains on the side surfaces of the LEDs 110 and lightemitting from the side surfaces of the LEDs 110 also passes through thecoating 132 and its phosphor particles. This results in conversion of atleast some of the side emitting light, which can provide LED chips 110having more consistent light emitting characteristics at differentviewing angles.

Following singulation, the LED chips 110 can be mounted in a package, orto a submount or printed circuit board (PCB) without the need forfurther processing to add phosphor. In one embodiment thepackage/submount/PCB can have conventional package leads with thepedestals 128 electrically connected to the leads. A conventionalencapsulation can then surround the LED chip 110 and electricalconnections.

While the above coating process provides one exemplary method offabricating the solid state light emitting devices according toembodiments of the present invention that include an LED and a phosphorcomposition, it will be appreciated that numerous other fabricationmethods are available. For example, U.S. patent application Ser. No.11/899,790, filed Sep. 7, 2007 (U.S. Patent Application Publication No.2008/0179611), the entire contents of which are incorporated herein byreference, discloses various additional methods of coating a phosphorcomposition coating onto a solid state light emitting device. In stillother embodiments, light emitting devices an LED chip that may bemounted on a reflective cup by means of a solder bond or conductiveepoxy, and the phosphor composition may comprise an encapsulant materialsuch as, for example, silicone that has the phosphors suspended therein.This phosphor composition may be used, for example, to partially orcompletely fill the reflective cup. Thus, the phosphor may be on the LEDor may be remote and optically coupled to the LED.

It is understood that although the present invention has been describedwith respect to LEDs having vertical geometries, it may also be appliedto LEDs having other geometries such as, for example, to lateral LEDsthat have both contacts on the same side of the LED chip.

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, the present specification, including the drawings, shall beconstrued to constitute a complete written description of allcombinations and subcombinations of the embodiments described herein,and of the manner and process of making and using them, and shallsupport claims to any such combination or subcombination.

While embodiments of the present invention have primarily been discussedabove with respect to solid state light emitting devices that includeLEDs, it will be appreciated that according to further embodiments ofthe present invention, laser diodes and/or other solid state lightingdevices may be provided that include the phosphor compositions discussedabove. Thus, it will be appreciated that embodiments of the presentinvention are not limited to LEDs, but may include other solid statelighting devices such as laser diodes.

In the drawings and specification, there have been disclosed embodimentsof the invention and, although specific terms are employed, they areused in a generic and descriptive sense only and not for purposes oflimitation, the scope of the invention being set forth in the followingclaims.

1. A phosphor composition comprising Ca_(i-x-y)Sr_(x)Eu_(y)AlSiN₃,wherein x is in a range of 0.50 to 0.99 and y is less than 0.013.
 2. Thephosphor composition according to claim 1, wherein the phosphorcomposition comprises at least 1% by weight of silicon aluminumoxynitride.
 3. The phosphor composition of claim 2, wherein the siliconoxynitride comprises Si₂Al₄O₄N₄.
 4. The phosphor composition of claim 1,wherein the phosphor composition absorbs light at a wavelength in arange of 350 and 530 nm and emits peak frequencies at a wavelength in arange of 620 to 660 nm
 5. The phosphor composition of claim 1, wherein xis in a range of 0.50 to 0.90 and y is in a range of 0.001 and 0.013. 6.The phosphor composition of claim 1, wherein the Sr to Eu ratio in thephosphor composition is in a range of 25 to
 300. 7. The phosphorcomposition of claim 1, wherein the phosphor composition is present inparticulate form and at least 95% of the particles are elongated.
 8. Aphosphor composition comprising Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃, wherein xis in a range of 0.70 to 0.99 and y is in a range of 0.001 and 0.025. 9.The phosphor composition according to claim 8, wherein the phosphorcomposition comprises at least 1% by weight of silicon aluminumoxynitride.
 10. The phosphor composition of claim 8, wherein the siliconoxynitride comprises Si₂Al₄O₄N₄.
 11. The phosphor composition of claim8, wherein x is in a range of 0.70 to 0.99 and y is in a range of 0.001and 0.013.
 12. The phosphor composition of claim 8, wherein the Sr to Euratio in the phosphor composition is in a range of 25 to
 300. 13. Thephosphor composition of claim 8, wherein the phosphor composition ispresent in particulate form and at least 95% of the particles areelongated.
 14. A light emitting device, comprising: a solid statelighting source; and a phosphor composition that comprisesCa_(1-x-y)Sr_(x)Eu_(y)AlSiN₃, wherein x is in a range of 0.50 to 0.99and y is less than 0.013.
 15. The light emitting device of claim 14,wherein the LED emits a warm white light having a correlated colortemperature between about 2700K and 5400K.
 16. The light emitting deviceof claim 14, wherein the light emitting device has a CRI value ofgreater than
 90. 17. The light emitting device of claim 14, wherein theSr to Eu ratio in the phosphor composition is in a range of 25 to 300.18. The light emitting device of claim 14, wherein the phosphorcomposition is present in particulate form and at least 95% of theparticles are elongated.
 19. The light emitting device of claim 14,wherein the phosphor composition is present as particles having anaverage particle size in a range of 4 μm to 20 μm.
 20. The lightemitting device of claim 14, wherein the phosphor composition is presentas a single crystal.
 21. The light emitting device of claim 14, furthercomprising a green and/or yellow phosphor.
 22. The light emitting deviceof claim 14, wherein the phosphor composition comprises at least 1% byweight of silicon aluminum oxynitride.
 23. A light emitting device,comprising: a solid state lighting source; and a phosphor compositionthat comprises Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃, wherein x is in a range of0.70 to 0.99 and y is in a range of 0.001 to 0.025.
 24. The lightemitting device of claim 23, wherein the LED emits a warm white lighthaving a correlated color temperature between about 2700K and 5400K. 25.The light emitting device of claim 23, wherein the light emitting devicehas a CRI value of greater than
 90. 26. The light emitting device ofclaim 23, wherein the Sr to Eu ratio in the phosphor composition is in arange of 25 to
 300. 27. The light emitting device of claim 23, whereinthe phosphor composition is present in particulate form and at least 95%of the particles are elongated.
 28. The light emitting device of claim23, wherein the phosphor composition is present as particles having anaverage particle size in a range of 4 μm to 20 μm.
 29. The lightemitting device of claim 23, wherein the phosphor composition is presentas a single crystal.
 30. The light emitting device of claim 23, furthercomprising a green and/or yellow phosphor.
 31. The light emitting deviceof claim 23, wherein the phosphor composition comprises at least 1% byweight of silicon aluminum oxynitride.
 32. A method of forming aphosphor composition, the method comprising mixing nitrides of calcium,strontium, aluminum and silicon with a europium source composition toform a precursor mixture, heating the precursor mixture to a temperaturein a range of 1500 and 1800° C. in the presence of forming gas, in arefractory crucible, to produce a phosphor composition comprisingCa_(1-x-y)Sr_(x)Eu_(y)AlSiN₃, wherein x is in a range of 0.50 to 0.99and y is less than 0.013, wherein the phosphor composition furthercomprises at least one percent of a silicon aluminum oxynitride phase.33. The method of claim 32, wherein the precursor mixture is heated in asubstantial absence of water and oxygen.
 34. The method of claim 32,wherein the silicon oxynitride comprises Si₂Al₄O₄N₄.
 35. The method ofclaim 32, wherein the refractory crucible is substantially inert in thepresence of the forming gas mixture.
 36. The method of claim 32, whereinthe forming gas dynamically flows around the refractory crucible. 37.The method of claim 32, wherein the precursor mixture is heated at afirst temperature for at least 0.5 hours, heated to a second temperaturefor at least 0.5 hours, and then heated to a third temperature for atleast 0.5 hours.
 38. The method of claim 37, wherein the firsttemperature is 800° C., the second temperature is 1200° C. and the thirdtemperature is 1800° C.
 39. The method of claim 32, wherein the phosphorcomposition absorbs light at a wavelength in a range of 350 and 530 nmand emits peak frequencies at a wavelength in a range of 620 to 660 nm.40. The method of claim 32, wherein the phosphor composition is presentin particulate form and at least 95% of the particles are elongated. 41.A method of forming a phosphor composition, the method comprising mixingnitrides of calcium, strontium, aluminum and silicon with a europiumsource composition to form a precursor mixture, heating the precursormixture to a temperature in a range of 1500 and 1800° C. in the presenceof forming gas, in a refractory crucible, to produce a phosphorcomposition comprising Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃, wherein x is in arange of 0.70 to 0.99 and y is in a range of 0.001 and 0.025. whereinthe phosphor composition further comprises at least one percent of asilicon aluminum oxynitride phase.
 42. A phosphor composition comprisingCa_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ phosphor particles, wherein x<1 and y<1,and at least some of the Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ phosphor particlesare elongated.
 43. The phosphor composition of claim 42, wherein 50% ormore of the Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ phosphor particles areelongated.
 44. The phosphor composition of claim 42, wherein 75% or moreof the Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ phosphor particles are elongated.45. The phosphor composition of claim 42, wherein 95% or more of theCa_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ phosphor particles are elongated.
 46. Thephosphor composition of claim 42, wherein x is in a range of 0.5 and0.99 and y is in a range of 0.001 and 0.025.